| 1. |
- Fiorelli, R., et al.
(author)
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CMOS Front End for Interfacing Spin-Hall Nano-Oscillators for Neuromorphic Computing in the GHz Range
- 2023
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In: Electronics. - : MDPI AG. - 2079-9292. ; 12:1
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Journal article (peer-reviewed)abstract
- Spin-Hall-effect nano-oscillators are promising beyond the CMOS devices currently available, and can potentially be used to emulate the functioning of neurons in computational neuromorphic systems. As they oscillate in the 4-20 GHz range, they could potentially be used for building highly accelerated neural hardware platforms. However, due to their extremely low signal level and high impedance at their output, as well as their microwave-range operating frequency, discerning whether the SHNO is oscillating or not carries a great challenge when its state read-out circuit is implemented using CMOS technologies. This paper presents the first CMOS front-end read-out circuitry, implemented in 180 nm, working at a SHNO oscillation frequency up to 4.7 GHz, managing to discern SHNO amplitudes of 100 mu V even for an impedance as large as 300 ohm and a noise figure of 5.3 dB(300 ohm). A design flow of this front end is presented, as well as the architecture of each of its blocks. The study of the low-noise amplifier is deepened for its intrinsic difficulties in the design, satisfying the characteristics of SHNOs.
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| 2. |
- Kumar, Akash, et al.
(author)
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Robust Mutual Synchronization in Long Spin Hall Nano-oscillator Chains
- 2023
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In: Nano Letters. - 1530-6984. ; 23:14, s. 6720-6726
-
Journal article (peer-reviewed)abstract
- Mutual synchronizationof N serially connectedspintronic nano-oscillators boosts their coherence by N and peak power by N (2). Increasing thenumber of synchronized nano-oscillators in chains holds significancefor improved signal quality and emerging applications such as oscillatorbased unconventional computing. We successfully fabricate spin Hallnano-oscillator chains with up to 50 serially connected nanoconstrictionsusing W/NiFe, W/CoFeB/MgO, and NiFe/Pt stacks. Our experiments demonstraterobust and complete mutual synchronization of 21 nanoconstrictionsat an operating frequency of 10 GHz, achieving line widths 79,000. As the number of mutually synchronizedoscillators increases, we observe a quadratic increase in peak power,resulting in 400-fold higher peak power in long chains compared toindividual nanoconstrictions. While chains longer than 21 nanoconstrictionsalso achieve complete mutual synchronization, it is less robust, andtheir signal quality does not improve significantly, as they tendto break into partially synchronized states.
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| 3. |
- Rajabali, M., et al.
(author)
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Experimental and molecular dynamics studies of an ultra-fast sequential hydrogen plasma process for fabricating phosphorene-based sensors
- 2021
-
In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11
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Journal article (peer-reviewed)abstract
- Low concentration phosphorene-based sensors have been fabricated using a facile and ultra-fast process which is based on an exfoliation-free sequential hydrogen plasma treatment to convert the amorphous phosphorus thin film into mono- or few-layered phosphorene sheets. These sheets have been realized directly on silicon substrates followed by the fabrication of field-effect transistors showing the low leakage current and reasonable mobility for the nano-sensors. Being capable of covering the whole surface of the silicon substrate, red phosphorus (RP) coated substrate has been employed to achieve large area phosphorene sheets. Unlike the available techniques including mechanical exfoliation, there is no need for any exfoliation and/or transfer step which is significant progress in shortening the device fabrication procedure. These phosphorene sheets have been examined using transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Raman spectroscopy and atomic-force microscopy (AFM). Electrical output in different states of the crystallization as well as its correlation with the test parameters have been also extensively used to examine the evolution of the phosphorene sheets. By utilizing the fabricated devices, the sensitivity of the phosphorene based-field effect transistors to the soluble L-Cysteine in low concentrations has been studied by measuring the FET response to the different concentrations. At a gate voltage of − 2.5 V, the range of 0.07 to 0.60 mg/ml of the L-Cysteine has been distinguishably detected presenting a gate-controlled sensor for a low-concentration solution. A reactive molecular dynamics simulation has been also performed to track the details of this plasma-based crystallization. The obtained results showed that the imparted energy from hydrogen plasma resulted in a phase transition from a system containing red phosphorus atoms to the crystal one. Interestingly and according to the simulation results, there is a directional preference of crystal growth as the crystalline domains are being formed and RP atoms are more likely to re-locate in armchair than in zigzag direction.
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| 4. |
- Kumar, Akash, et al.
(author)
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Fabrication of voltage-gated spin Hall nano-oscillators
- 2022
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; :4, s. 1432-1439
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Journal article (peer-reviewed)abstract
- We demonstrate an optimized fabrication process for electric field (voltage gate) controlled nano-constriction spin Hall nano-oscillators (SHNOs), achieving feature sizes of <30 nm with easy to handle ma-N 2401 e-beam lithography negative tone resist. For the nanoscopic voltage gates, we utilize a two-step tilted ion beam etching approach and through-hole encapsulation using 30 nm HfOx. The optimized tilted etching process reduces sidewalls by 75% compared to no tilting. Moreover, the HfOx encapsulation avoids any sidewall shunting and improves gate breakdown. Our experimental results on W/CoFeB/MgO/SiO2 SHNOs show significant frequency tunability (6 MHz V-1) even for moderate perpendicular magnetic anisotropy. Circular patterns with diameter of 45 nm are achieved with an aspect ratio better than 0.85 for 80% of the population. The optimized fabrication process allows incorporating a large number of individual gates to interface to SHNO arrays for unconventional computing and densely packed spintronic neural networks.
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| 5. |
- Litvinenko, Artem, 1989, et al.
(author)
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Phase noise analysis of mutually synchronized spin Hall nano-oscillators
- 2023
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In: APPLIED PHYSICS LETTERS. - 0003-6951. ; 122:22
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Journal article (peer-reviewed)abstract
- The reduction of phase noise in electronic systems is of utmost importance in modern communication and signal processing applications and requires an understanding of the underlying physical processes. Here, we systematically study the phase noise in mutually synchronized chains of nano-constriction spin Hall nano-oscillators (SHNOs). We find that longer chains have improved phase noise figures at low offset frequencies (1/f noise), where chains of two and ten mutually synchronized SHNOs have 2.8 and 6.2 dB lower phase noise than single SHNOs. This is close to the theoretical values of 3 and 10 dB, and the deviation is ascribed to process variations between nano-constrictions. However, at higher offset frequencies (thermal noise), the phase noise unexpectedly increases with chain length, which we ascribe to process variations, a higher operating temperature in the long chains at the same drive current and phase delays in the coupling between nano-constrictions.
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